The heat capacity and nuclear spin-lattice relaxation of the quasi-one-dimensional compound (${\mathrm{C}}_6$${\mathrm{H}}_{11}$${\mathrm{NH}}_3$)Cu${\mathrm{Br}}_3$ have been measured for 1.5 $K<T<\mathrm{}7\mathrm{}$ K and magnetic fields up to 7 kG. All data are in good agreement with classical soliton theory, both for in-plane and inclined fields, yielding the first evidence of solitons in a ferromagnetic quantum $\mathrm{XY}$ chain.

• Received 7 November 1983

DOI:https://doi.org/10.1103/PhysRevB.29.2868